Penrith lost 22-14 to Newcastle in a preliminary final that the Knights finished with 12 players after Phoenix Crossland was sent off.
The Panthers' injury toll also threatens Australia's World Cup plans, with captain Nathan Cleary undergoing emergency surgery overnight for a compound leg fracture.
Penrith coach Ivan Cleary said his son also needed surgery on a right-foot stress fracture, which had prompted speculation before the match. The injuries rule Nathan out of national selection next month.
Ivan Cleary also revealed Dylan Edwards ruptured his posterior cruciate ligament in the first half, while Isaah Yeo has played for a month with a fully ruptured pectoral muscle that requires surgery.
Asked whether he would delay his operation, Yeo said, "I'm not sure," and added, "I'll have to talk to the club because it would affect the start of next season if I was to prolong it, that's a conversation for later next week with Ivan and the staff."
Even low-grade PCL tears can take months to heal without surgery. If Edwards is unavailable, James Tedesco is expected to start at fullback for Australia's World Cup defence, with Reece Walsh likely as cover.
Blaize Talagi also suffered a serious Achilles injury and will miss selection for Samoa at the World Cup.
"We were probably falling apart a little bit," Ivan Cleary said after the match.